During the last few decades, substantial effort has been expended and interest has developed in the formation and construction of products using foamed thermoplastic materials. Typically, these products are formed either by foamed extrusion or molding. However, regardless of which method is employed, production limitations exist on the size and shape in which products can be efficiently produced at competitive prices.
One example of the type of products produced using the extrusion process is the creation of hollow elongated cylindrical tubes formed from foamed thermoplastic material. These tubes are used in a wide variety of products, most typically as insulation for fluid carrying pipes or conduits.
Although the extrusion manufacturing process for forming foamed cylindrically shaped thermoplastic tubes has progressed over the years to an extremely efficient production system, tube diameters greater than about seven inches are incapable of being produced on conventional equipment. Even though a substantial market exists for large diameter tubes formed of thermoplastic material, this demand cannot be satisfied using conventional extrusion equipment. Large diameter foam tubes require manufacturers to invest in the purchase of extremely expensive manufacturing equipment, before this demand can be met using current technology.
In view of the substantial investment that must be made by manufacturing companies in obtaining equipment for satisfying the industry needs for larger diameter cylindrical tube members, the products produced to meet this demand are extremely expensive, when compared to the conventional price for smaller diameter thermoplastic tubes. However, in spite of the demand for such products and the industry desire for competitive prices, prior art technology has failed to provide a manufacturing method capable of producing large diameter cylindrical tubes in a cost effective, price competitive manner.
In addition to the industry demands for larger diameter, hollow, cylindrical tubes, substantial demand also exists for foamed thermoplastic material formed in large sheet form in a wide range of thicknesses. Generally, conventional extrusion equipment for forming foamed thermoplastic products is incapable of producing foamed polymer sheets having widths greater than about 12" with a thickness of about 1/2". Consequently, the demand for large width foam plastic sheet is incapable of being satisfied by conventional manufacturers. In order to satisfy the industry needs for this product, extremely expensive, custom designed equipment must be purchased, causing the large width foam sheet products produced thereby to be more costly. In addition, the return of capital for this investment is low.
Although the specialized manufacturers who own this expensive equipment are capable of producing foamed thermoplastic sheet material in large width configurations, these manufacturers are still limited in the thickness that can be produced in a single sheet. Typically, these prior art sheet extruders are capable of producing sheet material having a maximum thickness of 1/2".
Consequently, any customer desiring to have a final product thicker than 1/2", is required to have the product produced by employing a plurality of sheets which are cut to size and integrally bonded to each other in order to build up a final product to the desired thickness. As a result, additional manufacturing and handling expenses are incurred and the final product produced by these specialized procedures is substantially increased in cost.
In order to produce plank material in thicknesses greater than 1/2", a plurality of sheets must be laminated or bonded together in secondary processes, increasing the thickness of the profile by 1/2" with each process. Such lamination steps substantially increase the complexity of the manufacturing procedures as well as increasing the overall scrap rates.
In an attempt to enable plank material to be produced in thicknesses greater than 1/2", accumulators have been constructed and used with extruders. By employing an extruder/accumulator combination, the foamed plastic is transferred directly from the extruder in the accumulators until the accumulator is filled. Then, using a piston or ram, the accumulated plastic is forced out of the accumulator. Using this system, planks with thicknesses up to 2" can be achieved. However, this process is inefficient, since it must be run intermittently and cannot be operated continuously. Furthermore, a high scrap rate is obtained due to the intermittent stop/start process.
As is evident from these systems, in spite of the demand for improved manufacturing techniques, no effective prior art manufacturing system has been developed for reducing the costs involved.
Consequently, it is a principal object of the present invention to provide a method for manufacturing large diameter foam tubes and foam plastic sheet material, using a production method which is easily achieved, highly effective, and comparatively inexpensive.
Another object of the present invention is to provide a new manufacturing process having the characteristic features described above which enables larger diameter hollow cylindrical tubes and large foam sheet material to be produced in an extremely cost efficient manner.
Another object of the present invention is to provide a new manufacturing process having the characteristic features described above which is capable of being employed with minimum of manpower and optimum production rates.
Other and more specific objects will in part be obvious and will in part appear hereinafter.